Process for forming lightpolarizing images



359-320 Search Room y 7/ E. H. LAND ETAL I 2,423,504

PROCESS FOR FORMING LIGHT-POLARIZING IMAGES O K Filed Sept. 22, 1943 2 Sheets-Sheet 1 FIG I FIG 2 1 July 8, 1947. E. H; LAND ET AL PROCESS FOR FORMING LIGHT-POLARIZING IMAGES 2 Sheets-Sheet 2 Filed Sept. 22, 1943 FIG.

FIG.

612m %VENTORS BY w gmv Search Room 2,423,504

Patented July 8, 1947 PROCESS FOR FORMING LIGHT- POLARIZING IMAGES Edwin H. Land, Cambridge, Mass, and Dexter P. Cooper, Jr., Hyde Park, N. Y., assignors to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Application September 22, 1943, Serial No. 503,406

25 Claims.

This invention relates to processes for formin dichroic images or vectographs, particularly dichroic reproductions of photographic images.

One object of the invention is to provide a new process for forming dichroic reproductions of photographic images.

Another object is to provide a new process whereby single or multiple positive, dichroic contact prints may be made from a single, conventional, photographic, paper print.

A further object is to provide such a process wherein the paper print itself enters into the reaction whereby the dichroic image is produced.

A still further object is to provide such a process which is particularly adapted to the production of dichroic prints which may be combined as superimposed right and left eye stereoscopic images.

Still further objects are to provide new articles produced in accordance with the process of th'e invention, and new materials and solutions for use in the practice of said process.

Other objects and advantages will in part be apparent and in part be pointed out in the course of the following description of one or more embodiments of th invention which are given as non-limiting examples in connection with the accompanying drawings, in which:

Figure 1 represents a conventional silver image such as a. photographic paper print, of which it is desired to mak a positive dichroic reproduction;

Figure 2 is a diagrammatic view representing a convenient way of handling the various elements duringth'e transfer of the desired image from the print shown in Fig. 1 to the plastic sheet on which the dichroic image is to appear;

Figure 3 is a diagrammatic view in perspective illustrating the dichroic print prepared in accordance with the invention, as it appears when viewed without an analyzer;

Figure 4 is a similar view showing the same print as it appears when viewed with a suitable analyzer, having its transmission axis at right.

angles to the transmission axis of said print;

Figure 5 is a view similar to Fig. 1 showing a pair of stereoscopic paper prints, one of which is reversed from right to left with respect to the other and from which it is desired to make a dichroic stereoscopic print in accordance with the present, invention;

Figure 6 is a diagrammatic view showing a convenient way of handling the various elements during the transfer of the desired images from the paper prints shown in Fig. 5 to a plastic sh'eet on which the stereoscopic images are to appear; and

Figure 7 is a plan view showing a stereoscopic print prepared in accordance with the invention from the paper prints shown in Fig. 5.

In th preferred embodiment of the present invention, the prints which are the product thereof are produced on a sheet of plastic material, particularly a vinyl oxy compound such, for example, as polyvinyl alcohol, or a polyvinyl acetal. Of the materials falling Within this class, the preferred material is polyvinyl'alco h'ol, and prints or images formed in properly prepared sheets of that material possess the highest dichroism and hence are most suitable in the production of superimposed right and left eye stereoscopic images.

In order to obtain the best results with respect to dichroism in the prints of the present invention, at least the surface molecules of the plastic sheet should first be substantially oriented. This may conveniently be accomplished by softening the sheet, as for example by subjecting it to heat, and then stretching or extending the sheet until suitable orientation of the molecules has been obtained. In the case of polyvinyl alcohol, a. sheet formed by casting may be placed in satisfactory condition for the formation of dichroic images therein by extending to from two to five or six times its length. Alternatively, the surface molecules of one or both sides of a sh'eet of polyvinyl alcohol may be oriented as by the application of linear, frictional force thereto without orienting the molecules throughout the remainder of the sheet.

In accordance with the present invention it is proposed to reproduce dichroic images by a transfer process from silver or other metal salt images prepared by conventional photographic methods. Accordingly, in order to practice said process, it is necessary first to prepare such an image from the desired photographic negative. Any silver salt image will be found to be satisfactory for this purpose and conventional paper prints, comprising a suspension of silver in gelatin on a paper backing, have been found particularly advantageous in view of the low cost of their material and production. Moreover, they may be prepared long before the process of the invention is practiced and. stored indefinitely. Fig. 1 represents such a paper print of which it is desired to form a dichroic reproduction.

Assuming that the silver image to be reproduced has'been prepared, the first step of the process of the invention is to treat said image plied from any water-soluble cupric salt, and the iodide ions and at least a portion of the ammonia may be furnished by adding ammonium iodide to the solution. Additional ammonia may be supplied, if needed, from any ionizable ammonium compound, preferably an inexpensive compound such as ammonium chloride. The ammonium ions released by such compound may easily be converted to ammonia by adding to the solution any relatively strong base such, for example, as sodium hydroxide, which serves also to prevent the precipitation of copper hydroxide and the release of free iodine. The proportions of the above compounds in the solution may be varied within wide ranges. For purposes of illustration, however, the following formula is given as an example of a solution with which satisfactory results have been obtained, but it is to be understood that the proportions and compounds therein are to be interpreted as illustrative only and not in a limiting or critical sense.

Ammonium iodide, solution cc 250 Ammonium chloride, 20% solution cc 100 Sodium hydroxide, 10% solution cc 150 Cupric chloride, 10% solution cc 125 When a silver image is immersed in a solution having approximately the foregoing formula, it is bleached to a light slate blue in color and should be allowed to soak until said color change is complete, which should be accomplished in about thirty seconds. The precise reactions producing this result are not definitely known, but it appears that the silver is converted to silver iodide, and it is thought that the ammonia and cupric and iodide ions combine to form a complex compound, probably tetramine cupric iodide, which compound is adsorbed on or otherwise attached to the silver iodide, thus producing the slate blue color. The density of any unit area of the original image is determined by the amount of silver present in that area-the more silver, the darker the area. Accordingly, the amount of the above complex adsorbed in any unit area of the print depends upon the amount of silver initially deposited in that area.

It should be pointed out that the above step may, if desired, be divided into two parts. In the first, the silver in the image may be converted to a silver salt, preferably non-water soluble, by any conventional photographic bleaching or toning bath. As a second step, the bleached image may then be permitted to adsorb the cupric-ammonia-iodide complex from the foregoing solution. It is to be understood that the following claims are to be construed as covering either of these alternative methods for carrying out this part of the process of the invention.

After the foregoing reactions are completed, the next step is to remove from the gelatin of the print the excess solution and complex which has not been adsorbed on the silver iodide, as by washing in a solution which will not disturb the silver iodide or the complex adsorbed thereon. This may be doneby washing in plain water, but due to the degree of control which must be exercised to prevent removal of the complex adsorbed on the silver iodide, it is preferable to add to the washing solution small amounts of the ingredients used in the first solution. A satis-' factory bath for this purpose may be made up approximately as follows:

Ammonium iodide, 20% solution cc 107 Ammonium chloride, 20% solution cc Sodium hydroxide, 10% solution cc 119 Cupric chloride, 10% solution cc For best results, one part of the above solution should be mixed with seven parts of water, and the print will be sufficiently Washed after about thirty seconds therein. It will then comprise a suspension in a layer of gelatin, on the paper or other backing, of silver iodide or other silver salt having the above complex adsorbed thereon. It should be understood that the term adsorbed as used herein is to be construed as including the possibility of chemical combination. The amount of said complex present in any unit area will be proportional to the amount of silver originally present therein. Accordingly the image will be the same as the original silver image, but the variations in density therein will be rendered in varying tones of light slate blue.

The next step in the process is to treat the image with a solution which will release free iodine from the above mentioned complex, which may be accomplished by a variety of solutions which will act to break down the complex. A

simple method is to treat the complex with an' acid which will neutralize the ammonia to NH4. Alternatively, the same result may be secured by the use of an acid salt, or merely adding an ex cess of cupric chloride to the solution will produce the desired result. As anillustrative example, satisfactory results have been obtained with a solution made up approximately as follows:

Nitric acid, solution cc 1800 Cupric chloride, 10% solution cc 270 When the washed image is dipped in a solution such as the above example, it appears that the ammonia in the above complex is neutralized, thus breaking up the complex and leaving cupric iodide. 'Ilhis in turn undergoes an oxidation-reduction reaction and transforms to cuprous iodide, releasing free iodine, as is made apparent almost immediately by changing the color of the image from slate blue to orange-brown. The time required for this step of the treatment is relatively short, approximately ten seconds generally being sufficient.

After the foregoing steps are completed, the print should be placed with its emulsion side against the oriented surface of the polyvinyl a1- cohol or other plastic sheet, and the two sheets should be pressed together with relatively firm, even pressure. A convenient method for carrying out this step of the process is shown in Fig. 2, wherein element I0 represents the treated paper print, superimposed face down upon the oriented surface of a sheet of polyvinyl alcohol I2. The two sheets are shown as mounted for convenience on a flat surface such as M, and element 45 represents any device such as a rubber roller or squeegee for pressing the two sheets together with a relatively firm, even pressure.

During the above step, the iodine released from the complex transfers from the gelatin to the oriented surface of the plastic sheet. Moreover, since the amount of iodine present varies throughout the area of the gelatin layer, dependmitted by print 20.

liters ing. upon the density of the original image therein, the plastic sheet is difierentially stained proportionally to the density of the original image, thus producing a positive dichroic reproduction of the original silver image in the print. The image on the paper print will at some time be found to change in color from orange-brown to a relatively faint yellow having a bleached appearance.

When the foregoing steps are completed, the two sheets should be separated, and the dichroic print will then be finished. It will have approximately the appearance illustrated in Fig. 3, wherein print 20 bears a positive reproduction in dichroic areas of the image in element l2, but the image will be relatively faint when viewed as in Fig. 3 without an analyzer. This is due to the fact that print 20, speaking in terms of optics, is merely an imperfect polarizer, which absorbs some of the light vibrating in one direction proportionally to the variations in density of its stained areas, but transmits the remainder of that component and all of the component vibrating in the opposite direction. In order, therefore, to see the image thereon properly, it should be viewed through a suitable crossed analyzer.

Such an arrangement is shown in Fig. 4, wherein a polarizing element 39 of uniform polarization characteristics is shown superimposed on print 20, with its transmission axis at right angles to that of the print, as indicated by arrows 25 and 35. The result is that analyzer 30 absorbs all of that component of the light which is freely trans- On the other hand, the analyzer transmits the other component of the light, which is the component differentially absorbed by the print, and will thus cause the image on print 20 to appear in as complete detail and with as high a degree of clarity as the original image in print l2.

One of the features of the process of the present invention is that it may be used to make multiple dichroic prints from a single silver image such as a paper print. This is due to the fact that none of the silver iodide formed during treatment in the first solution is used up in the printing step. Apparently all that happens is that when the print is treated with the last solution. the complex formed in the first solution is broken down and the iodine attached to the cupric and ammonium ions is released. The silver iodide, however, appears .to remain in substantially the same condition as before. Therefore, after the transfer step is completed, the paper print may be returned to the first solution, with the resulting reformation of the complex, and the entire process can then be repeated virtually indefinitely or until the print may become worn out from handling.

Another feature of the present invention is that after completion of the above outlined process, the paper print may, if desired, be reconverted to its original form. This is done by re- Water cc 1000 Sodium sulphate grams '75 Sodium carbonate do 25 Potassium bromide do .5 Metol" do 5 As has already been pointed out, the foregoing example has been given only by way of illustration, and many variations may be made therein without departing from the scope of the invention. For example, instead of cupric chloride, other water-soluble cupric salts such as copper sulphate may be used. In place of ammonia, other bases may be used, such for example as organic amines. Similarly, in place of the nitric acid in the iodine-release bath, there may be used other acids such as hydrochloric or sulfuric acid or other agents, for example hydrogen peroxide, which will bring about the desired release of free iodine. Furthermore, it has been found advantageous to modify this step of the process by eliminating the iodine-release bath and instead to incorporate, as by casting, a suitable agent such as nitric acid in the oriented plastic sheet. With this modification, the release and transfer of the iodine take place substantially simultaneously, thus eliminating any possibility that the free iodine may run and insuring clearer prints.

Other similar modifications will be apparent to' those skilled in the art and are to be understood as coming within the scope of the invention.

The process of the invention has thus far been described as applied to single prints. It should be pointed out, however, that it may easily be practiced in connection with stereoscopic negatives. For example, a pair of conventional paper prints may be prepared from a pair of stereoscopic negatives, and the above process may be practiced separately with each of the said paper prints to produce separate right and left eye dichroic images having their transmission axes substantially at right angles to each other. The two separate dichroic reproductions may then be superimposed to form a single stereoscopic print.

An alternative method of practicing the invention in connection with stereoscopic negatives is illustrated in Figs. 5, 6 and 7. Elements 40 and 50 in-Fig. 5 represent conventional silver image paper prints of a pair of stereoscopic negatives. It will be noted, however, that one of said prints has been reversed from right to left with respect to the other, that is to say, the two prints are substantially mirror prints with the exception that the images thereon are slightly different and may be relatively offset by reason of their stereoscopic relation. This result may be obtained dur- I 'shown in Fig. 5, and it is assumed that each has been treated in the three solutions described above in connection with single prints. Element 60 represents a suitably prepared sheet of plastic such as polyvinyl alcohol, and by suitably prepared it is meant that the molecules of one surface of said sheet have been oriented in a direction substantially at right angles to the molecules of the other said surface. This result may be accomplished in one of two ways. The sheet may comprise a lamination of two separate sheets of polyvinyl alcohol which have been separately stretched as described above and then laminated together or to a central supporting layer with the stretch axes thereof substantially crossed. Alternatively, element 60 may comprise a single sheet of polyvinyl alcohol which has had the molecules on each surface thereof oriented in directions substantially at right angles to each other.

In carrying out the transfer step of the process, each of paper prints 40 and 50 is placed with its emulsion side against the surface of the polyvinyl alcohol or other oriented plastic sheet to form a sandwich, care being taken to secure accurate relative registering between the images on prints 60 and 50. The three elements should then be pressed relatively firmly and evenly together by any suitable means such, for example, as the pair of rubber rollers 65 illustrated in Fig. 6, wherein paper prints 40 and 50 are represented as forming the outside layers of a sandwich and with their emulsion sides in contact with the surfaces of a suitably oriented plastic sheet 60. If it is desired to use prints 80 and 50 in the production of multiple stereoscopic dichoic prints, it will be found advantageous to secure them together along one edge by any suitable hinge-like means such as adhesive tape or a suitable clip means, as is indicated at 66 in Fig. 6.

Fig. 7 represents a stereoscopic print produced in accordance with the above outlined steps. When viewed without a suitable stereosopic viewing device, it will be noted that on one surface of plastic sheet 60 appears the image 10 transferred from paper print 40, and the transmission axis of the dichroic areas therein is represented as parallel to the arrow 45. On the other surface of sheet 60 there is indicated, in dotted lines, a dichroic reproduction of the image transferred from paper print 50, with the transmission axis thereof indicated by arrow 55 as at right angles to the transmission axis of image 70. When the print shown in Fig. 7 is viewed through a suitable viewing device such as a pair of glasses provided with polarizing lenses having their transmission axes relatively perpendicular and parallel respectively to one and the other of the transmission axes of images 10 and 15, each eye will see only one of said images, which will thus produce the desired three-dimensional effeet.

It should be pointed out that the stereosopic print shown in Fig. 7 will be substantially the same in appearance and operation whether ele ment 60 is a laminated sheet of separately stretched components or a single sheet having its opposite surfaces difierently oriented. I should also be pointed out that if the right and left eye dichroic images are prepared separately and then assembled in superimposed relation, in accordance with the first method outlined above, the resulting print will be'substantially the same as that shown in Fig, 7, with the exception that the image therein corresponding to the image 15 will preferably lie on that surface of the separate sheet Whereon it is reproduced Which is adjacent to or laminated to the sheet bearing image 70, instead of lying on the outer or bottom surface of element 60 in the manner indicated in Fig. 7.

With respect to the orientation of the plastic sheets used herein, it should be pointed out that it is essential that only the portions thereof penetrated by the iodine solution require molecular orientation. It is of no importance whether or not the molecules in unstained portions of the sheet be oriented. It is to be understood, therefore, that whenever such sheets are specified herein and in the following claims as being substantially'molecularly oriented, this term is to be interpreted as meaning that the depth of orientation is at least sufficient to include all portions penetrated by the iodine solution, and therefore as including both surface oriented and stretched sheets.

As has been previously stated, the foregoing description is only illustrative of certain embodiments of the present invention. It must again be emphasized that each step therein is a variable, and that none of the ingredients, times or proportions for any step are critical except in so far as they may be made so by the other variables. For example, virtually any compounds may be used in the various solutions provided they will supply the desired cupric, ammonium and iodide ions. Furthermore, the concentrations in the solutions may be varied through a wide range, the necessary amount of any particular compound being determined primarily by the amount of the other compounds present. The specific examples given comprise together a complete process with which excellent results have been obtained. However, great variation is possible and virtually any degree thereof in one or more solutions or steps can be compensated for in the other steps. It is accordingly obvious that no set rules can be given.

What is claimed is:

l. Th method of .producing dich'roic images which comprises converting a silver image into an insoluble silver salt image, converting said second named image into an image comprising a 2. The method of producing dichroic images I which comprises converting a. silver image into an image comprising a compound containing releasable iodine, treating said last named image with an agent adapted to release free iodine therefrom, and pressing said image evenly against a molecularly oriented sheet comprising a lighttransmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet.

3. The method of producing dichroic images which comprises converting a silver image into an insoluble silver salt image, combining said silver salt image with a compound containing releasagent adapted to release free iodine therefrom, and pressing said image evenly against a moleccularly oriented sheet comprising a light-transmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet.

5. The method of producing dichroic images which comprises converting a silver image into an image comprising silver iodide and cupric iodide, treating said last named image with an agent adapted to release free iodine therefrom, and pressing said image evenly against a molecularly oriented sheet comprising a light-transmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet.

6. The method of producing dichroic images which comprises converting a silver image into an insoluble silver salt image, converting said second named image into an image comprising a [compound containing releasable iodine, incorporating in a molecularly oriented sh'eet comprising a light-transmitting polyvinyl oxy compound an agent adapted to release free iodine from said last named image, and pressing said last named image while wet into even contact with said sheet to release iodine from said image and transfer it to said sheet.

7. The method of producing dichroic images 7 which comprises converting a silver image into an image comprising a compound containing releasable iodine, incorporating in a molecularly oriented sheet comprising a light-transmitting polyvinyl oxy compound an agent adapted to release free iodine from said last named image, and pressing said last named image while wet into even contact with said sheet to release iodine from said image and transfer it to said sheet.

8. The method of producing dich'roic images which comprises converting a silver image into an image comprising silver iodide and cupric iodide, treating said last named image with an acid to release free iodine therefrom, and pressing said image evenly against a molecularly oriented sheet comprising a light-transmitting polyvinyl oxy compound to transfer said iodine from saidimage to said sheet.

9. The method of producing dichroic images which comprises converting a silver image into an imag comprising silver iodide and cupric iodide, incorporating in a molecularly oriented sheet comprising a light-transmitting polyvinyl oxy compound an agent adapted to release free iodine from said last, named image, and pressing said last named image while wet into even contact with said sheet to release iodine from said image and transfer it to said sheet.

10. The method of producing dichroic images which comprises converting a silver image into an insoluble silver salt image, converting said second named image into an image comprising a compound containing releasable iodine, treating said last named image with an agent adapted to release free iodine therefrom, and pressing said image evenly against a molecularly oriented sheet comprising polyvinyl alcohol to transfer said iodine from saidimage to said sheet.

11. The method of producing dichroic images which comprises treating a silver image with a solution comprising cupric ions, iodid ions and ammonia, treating the resulting image with an agent adapted to release free iodine therefrom, and then pressing said image evenly against a molecularly oriented sheet comprising a, lighttransmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet.

12. The method of producing dichroi-c images which comprises treating a silver image with a solution comprising cupric ions, iodide ions and ammonia, treating the resulting image with an agent comprising an acid to release free iodine therefrom, and then pressing said image evenly against a molecularly oriented sheet comprising a light-transmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet.

13. The method of producing dichroic images which comprises treating a silver image with a. solution comprising cupric ions, iodide ions and ammonia, washing the resulting image with a relatively very dilute solution comprising the same ingredients, then treating the resulting image with an agent adapted to release free iodine therefrom, and then pressing said image evenly against a molecularly oriented sheet comprising a lighttransmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet.

14. The method of producing dichroic images which comprises treating a silver image with a solution comprising cupric ions, iodide ions and ammonia, washing the resulting image with a relatively very dilute solution comprising the same ingredients, then treating the resulting image with an agent comprising an acid to release free iodine therefrom, and then pressing said image evenly against a molecularly oriented sheet comprising a light-transmitting polyvinyl oxy compound to transfer said iodine from said image to which comprises treating a silver image with a solution comprising cupric ions, iodide ions and ammonia, washing the resulting image with a relatively very dilute solution comprising the same ingredients, then treating the resulting image with an agent comprising an acid to release free iodine therefrom, and then pressing said image evenly against a molecularly oriented sheet comprising polyvinyl alcohol to transfer said iodine from said image to said sheet.

16. The method of producing a dichroic stereoscopic print from a pair of predetermined, stereoscopic negatives which comprises forming a positive silver image of one of said negatives, forming from the other of said negatives a positive silver image reversed with respect to the first-said image, converting said silver images into insoluble silver salt images, converting said second-named images into images comprising a compound containing releasable iodine, treating said last named images with an agent adapted to release free iodine therefrom, and then pressing said images evenly against the opposite surfaces of a molecularly oriented sheet comprising a transparent olyvinyl oxy compound, the direction of molecular orientation on one surface of which is substantially perpendicular to the direction of molecular orientation on the other said surface, said images being held in relative register during said lastnamed step.

17. The method of producing a dichroic stereoscopic print from a pair of predetermined, stereoscopic negatives which comprises forming a positive silver image of one of said negatives, forming fronithe' other of said negatives a positive silver image reversed with respect to the first-said image, converting said silver images into images comprising a compound containing releasable iodine, treating said last named images with an agent adapted to release free iodine therefrom, and then pressing said images evenly against the opposite surfaces of a molecularly oriented sheet 11 comprising a transparent polyvinyl oxy compound, the direction of molecular orientation on one surface of which is substantially perpendicular to the direction of molecular orientation on the other said surface, said images being held in relative register during said last-named step.

18; The method ofproducing a dichroic stereoscopic print from a pair of predetermined, stereoscopic negatives which comprises forming a positive silver image of one of said negatives, forming from the other of said negatives a positive silver image reversed with respect to the first-said image, treating said silver images with a solution comprising cupric ions, iodide ions and ammonia, treating the resulting images with an agent adapted to release free iodine therefrom, and then pressing said images evenly against the opposite surfaces of a molecularly oriented sheet comprising a transparent polyvinyl oxy compound, the direction of molecular orientation on one surface of which is substantially perpendicular to the direction of molecular orientation on the other said surface, said images being held in relative register during said last-named step.

19. The method of producing a dichroic stereoscopic print from a pair of predetermined, stereoscopic negatives which comprises forming a positive silver image of one of said negatives, forming from the other of said negatives a positive silver image reversed with respect to the first said image, treating said silver images with a solution comprising cupric ions, iodide ions and ammonia, treating the resulting images with an agent comprising an acid to release free iodine therefrom, and then pressing said images evenly against the opposite surfaces of a molecularly oriented sheet comprising a transparent polyvinyl oxy compound, the direction of molecular orientation on one surface of which is substantially p rpendicular to the direction of molecular orientation on the other said surface, said images being held in relative register during said last-named step.

20. The method of producing dichroic images which comprises converting a silver image into an image comprising a compound containing releasable iodine, treating said last named image with an agent adapted to release free iodine therefrom,

. pressing said image evenly against a molecularly transmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet and repeating said last three named steps to produce a multiplicity of dichroic images.

22. The method of producing dichroic images which comprises treating a silver image with a solution comprising cupric ions, iodide ions and ammonia, treating the resulting image with an agent adapted to release free iodine therefrom, then pressing said imag evenly against a molecularly oriented sheet comprising a, light-transiodine from said image to said sheet and re peating said last three named steps to produce a multiplicity of dichroic images.

23. The method of producing dichroic images which comprises converting a silver image into an image comprising a compound containing releasable iodine, treating said last named image with an agent adapted to release free iodine therefrom, pressing said image evenly against a molecularly oriented sheet comprising a lighttransmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet and then reconverting said image to its original condition.

24. The method of producing dichroic images which comprises converting a silver image into an image comprising a compound containing releasable iodine, treating said last named image with an agent adapted to release free iodine therefrom, pressing said image evenly against a molecularly oriented sheet comprising a lighttransmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet and then reconverting said image to its original condition by developing in a high potential developer.

25. The method of producing dichroic images which comprises converting a silver image into an image comprising a compound containing releasable iodine, treating said last named image with an agent adapted to release free iodine therefrom, pressing said image evenly against a molecularly oriented sheet comprising a lighttransmitting polyvinyl oxy compound to transfer said iodine from said image to said sheet and then developing said image to reconvert it to its original condition.

EDWIN H. LAND.

DEXTER P. COOPER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,059,917 Tauleigne Apr. 22, 1913 2,070,222 Brewster Feb. 9, 1937 1,957,045 Kelly May 1, 1934 1,214,940 Miller Feb, 6, 1917 1,992,169 Brewster Feb. 26, 1935 2,327,822 Russell Aug. 24, 1943 1,945,658 Roessler Feb. 6, 1934 2,099,297 Clement Nov. 16, 1937 2,329,543 Land Sept, 14, 1943 2,315,373 Land Mar. 30, 1943 2,108,261 Jamieson Feb. 15, 1938 2,019,718 Mannes et al. Nov, 5, 1935 2,141,354 Gundelfinger Dec. 27, 1938 2,183,661 Trimble Dec. 19, 1939 FOREIGN PATENTS Number Country Date 100,098 Great Britain May 10, 1917 526,780 Great Britain Sept. 25, 1940 OTHER REFERENCES Mellor, Treatise on Inorganic and Theoretical Chemistry, vol. III (1923), Longmans, Green 8: C0,, New York, page 208, last paragraph, and page 209. 

